Many electrical devices include some audio capability and thus include some audio circuitry. For example, portable electronic devices, such as smartphones or tablet computers or the like, typically include an audio circuit, such as an audio codec or the like, that can drive one or more audio transducers of the host device. Such devices may also have the ability to provide audio signals for driving an external audio load, e.g. an audio transducer of a peripheral device that may, in use, be removably connected to the device via some suitable connector, such as a jack plug and socket arrangement or some other mating connector such as a USB connector or the like. The audio circuit may therefore be connected to one or more contacts or a device connector, e.g. a jack socket, for outputting or receiving audio signals.
It has been recognised that in some cases such an audio circuit may be subject to a possible electrical overstress. Electrical overstress (EOS) refers to an electrical stimulus being applied which is greater than a rated operating range of the circuit. Electrical overstress may occur from a variety of causes, such as electrostatic discharge or power fluctuations or the like. For an audio circuit of the type described above an electrical overstress could possibly be applied via the device connector.
At least some audio circuits may include some protection circuitry designed to try to protect the circuit in the event of an applied overvoltage or overcurrent. In the event of a voltage/current surge at a contact of the audio circuit, the protection circuit may operate. In some instances the protection circuitry will operate correctly and once the surge has dissipated the audio circuit may continue to function normally. In some instances however operation of the protection circuitry may disrupt the operation of the audio circuit, leading to a temporary defective operating state or the protection circuitry may not be able to prevent damage to the audio circuit which could result in a permanent defective state.